I couldn't say with any certainty, but I bet you're on to something...would seem to make sense, at any rate. I would guess the cold helps take out some of the slack within the structure, which when coupled with tension balancing efforts I'm guessing could help with the intentional use of the fascia.

I don't know squat about the language, but for the practice I enjoy what I perceive as an increase in sensation over the surface of my skin (never mind the general "WAKE UP!" my body screams at me), like wearing a cold suit. The cold stands out to my attention giving me a better general sense of my whole body as well as specfic points on it (increased proprioceptive awareness?). The most obvious benefit I noticed when I did river misogi regularly was the effect on my nervous system, which I atttribute to constantly trying to calm myself (stop shaking; breathe slowly and deeply) while my body is trying to do the opposite. I became a lot better at becoming very still...relating to the natural sway we all have when trying to stand perfectly still.
My two bits! Cheers y'all!

...I know sensei Barrish describes Misogi no Gyo as a way of yang-izing the body, increasing "density" to our actions.